Update the React 18 documentation (vercel#32896)

Currently you don't need to enable `concurrentFeatures` to start using React 18, this PR makes the docs more clear on that.

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`

Author: shuding

docs/advanced-features/react-18.md

@@ -12,6 +12,8 @@ Ensure you have the `rc` npm tag of React installed:
 npm install next@latest react@rc react-dom@rc
 ```
 
+That's all! You can now start using React 18's new APIs like `startTransition` and Suspense in Next.js.
+
 ### Enable SSR Streaming (Alpha)
 
 Concurrent features in React 18 include built-in support for server-side Suspense and SSR streaming support, allowing you to server-render pages using HTTP streaming.